A film in a plastic or a cardboard package or an image plate in a cassette have been used so far in intraoral dental radiography. The image plate has been either free in the openable cassette or fixed by glueing to a rigid cassette equipped with a slide plate.
U.S. Pat. No. 5,466,561 describes a solution, in which the image plate is placed into a cover letting through X-rays but not visible light, which comprises a closed protective bag of plastic film. The image plate including the bag-like cover is thinner and thus more pleasant to the patient than a cassette containing the image plate, and compared to a conventional intraoral film, it has the advantage of a lower sensitivity to visible light.
According to U.S. Pat. No. 5,466,561 the image plate is placed into the cover as such for the time of the X-raying. In this connection there have been problems caused by scratches on the plastic film on the image surface of the plate when the plate is being handled and scanned, as well as finger prints on the image surface which will be visible on the resulting picture. Besides the image surface, the edges of the plate have been easily damaged and broken. The edges of the plate have in fact been protected with a coated plastic film, however this has proved an unsufficient protection. When the edge is broken, the RIM substance within the plate, such as a poisonous barium compound, will appear, and may be hazardous to the patient or the person who handles the plate. An unprotected RIM substance does not resist sterilization carried out with ethanol for instance, the entire plate being destroyed in that case. The operating life of the image plate may be shortened by these wear and damage problems.